Air pollution is a major problem in most urban areas. It is a fact that air pollution is the major problem currently facing the automobile industry. The main air pollutants from diesel engine exhaust gas are carbon monoxide (CO), nitrogen oxides (NOx), carbon dioxide (CO.sub.2), hydrocarbons (HC) and particulate matter (PM). The dangers of NOx, CO and hydrocarbons to both the environment and general population are well known. Now NOx is treated as an ozone precursor. This certainly means more stringent controls for NOx. Federal, state and local regulators regularly lower the permissible level for NOx. Therefore, NOx remains the main problem to be solved, and to a certain extent, attention must also be paid to carbon monoxide and particulate matter which causes opacity.
NOx remains a problem pollutant. It can be reduced by exhaust gas recirculation (EGR), but such recirculation has a number of disadvantages including major engine wear from sulfuric acid derived from the sulphur inherent on fuels; contamination of the lubricant from soot particles; and increased specific diesel fuel consumption. It is seemingly evident that EGR cannot resolve the problem of lowering NOx formation without affecting engine performance and reliability.
Another way of reducing exhaust gas NOx emissions is cooling the combustion by introducing water into the combustion. This has been tested and found to result in decreased NOx production. Introduction of water into the diesel fuel has been attempted in two ways in the past. The first was to emulsify the water into the diesel fuel. This requires special chemicals, such as wetting agents. In addition, a special pump and a mixer are required. Another method is direct injection of the water into the cylinder. In very large engines, such as marine engines, separate injectors are employed. In this case, the water injection system is a substantial duplicate of the already existing diesel fuel injection system and is controlled in a similar manner. A more recently developed system includes the injection of the diesel fuel and the water into the cylinder with the same injector. The two liquids are layered in the injector and are sequentially injected. This is a sophisticated system which requires a considerable amount of attention, and is suitable only for those large engines where there are competent engine operators present, such as in marine and large stationary engine installations.
The disadvantages of water injection systems as tested in diesel engines using a water/diesel fuel mixture include corrosion of the diesel fuel pump, diesel fuel injectors and connecting tubing. When water is directly injected into the cylinders under high pressure, it also results in increased cylinder wear. The provision of separate water injectors in diesel engines increases the cost of an engine and results in more complicated operation, increased maintenance costs, and reduced engine reliability. However, the employment of water in diesel engine operation does reduce its NOx output and, thus, would be desirable if the disadvantages could be overcome.
The present invention has been developed from a thorough analysis of the nature of exhaust gas emissions formation. The main goals of this invention consist in providing a system which does not require emulsification or special injectors, but provides a system wherein a simple mixer provides the proper water/diesel fuel mixture. The mixer and the conventional fuel pump supplying the injectors mix into the diesel fuel a small quantity of water in a known water/diesel fuel ratio. This water/diesel fuel mixture starts mixing in a special mixing chamber before the mixture comes to the fuel pump where the liquids are further mixed. The mixture then goes to the diesel injectors and then to the cylinders. Only a small water tank, the above-mentioned mixing chamber, a small mixed water/diesel fuel return tank and control sensors are required in addition to the existing equipment.